1. Field of the Invention
The present invention relates to an ink supplying mechanism for an ink ribbon incorporated in printing apparatuses including a serial dot impact printer.
2. Description of the Related Art
Some conventional dot impact printers incorporate an ink ribbon cartridge equipped with an ink supplying mechanism. FIG. 16 illustrates one such printer disclosed by Japanese Patent Laid Open No. H08-192560. Referring to FIG. 16, a conventional dot impact printer is equipped with an ink ribbon cartridge 112D that holds an endless type ink ribbon 111 impregnated with a liquid ink. A printhead 113 is mounted on a carriage unit 115. The ink ribbon 111 extends through a gap between a printhead 113 and paper 114. The wires (not shown) of the printhead 113 impact the ink ribbon 111 to print on the paper 114.
The amount of ink (not shown) in the ink ribbon 11 decreases as printing is carried on. An ink tank 120 supplies the ink to the ink ribbon 111.
The carriage unit 115 is driven by a spacing motor 116 and pulleys 117a and 117c to move leftward and rightward reciprocally across the paper 114.
A spacing belt 118 is disposed about the pulleys 117a and 117c. The carriage unit 115 is fixed to the spacing belt 116. The spacing motor 116 rotates to cause the carriage unit 115 to move in directions shown by arrows A and B. The ink ribbon cartridge 112D is fixed to side frames 119a and 119b, and accommodates an ink tank 120 with an ink replenishing strip 121 in contact with the ink ribbon 111. Thus, the ink is directed from the ink tank 120 to the ribbon 111 by capillary action.
A transfer roller 122 is in rotatable contact with the ink replenishing strip 121. A drive roller 123 rotates in pressure contact with the transfer roller 122 so that when the drive roller 123 rotates, the transfer roller 122 will also rotate. When printing is performed, the spacing motor 116 drives the carriage unit 115 to move leftward and rightward so that the printhead 113 moves across the paper 114.
The pulleys 117a and 117b are mounted on the shaft of the spacing motor 116. The pulley 117b includes gear teeth in mesh with a gear 124a, which in turn is in mesh with a gear 124b. When the ink ribbon cartridge is attached to the printer, the gear 124b moves into meshing engagement with a drive shaft located on a body of the dot impact printer. The drive shaft fits in a drive roller 123 so that the drive shaft is concentric to the drive roller 123. The spacing motor 116 drives the pulley 117b, gear 124a, and gear 124b to rotate, thereby driving the drive roller 123 in rotation.
Thus, the ink ribbon 111 advances through a gap between the transfer roller 122 and the drive roller 123. The ink replenishing strip 121 is in pressure contact with the transfer roller 122.
The ink is supplied from the ink tank 120 to the transfer roller 122 through the ink replenishing strip 121. Then, the ink is transferred onto the ink ribbon 111 from the transfer roller 122. In this manner, the ink is replenished to the ink ribbon 111.
However, the ink replenishing strip 121 of the aforementioned conventional configuration is in contact with the transfer roller 122 at all times. Therefore, if the ink ribbon cartridge 112D is left unused for a long period of time, an excess amount of ink stays only at an area where the transfer roller 122 is in contact with the replenishing strip 121. The ink ribbon 111 that has absorbed excess ink will result in uneven density of printed images such as spread of ink at the beginning of a new printing operation shortly after replacement of the ink ribbon cartridge 112D, which shortens the useable life time of the ink ribbon cartridge 112D due to excess initial density of printed characters.